1. Field of the Invention
The present invention relates to a method of writing identifying information on a wafer, wherein the identifying information is written by photolithography on the wafer used for forming thin-film elements.
2. Description of the Related Art
Thin-film elements manufactured through thin-film forming techniques include those manufactured by forming a plurality of thin-film elements on a wafer (substrate) through the use of the thin-film forming techniques and then separating the wafer into the individual thin-film elements. Such thin-film elements include semiconductor elements and thin-film magnetic heads.
Typically, the above-mentioned thin-film elements are manufactured through a plurality of steps. In this case, in appropriate steps, alignment marks are formed on the wafer for alignment performed in the following step. Such alignment marks may be made of patterned films that are patterned through the use of photolithography, for example. Japanese Published Patent Application 2002-184672 discloses a technique in which alignment marks for a batch exposure apparatus and alignment marks for a reducing exposure apparatus are formed on a wafer in a first photolithography step.
Typically, wafer identifying information and element location identifying information are written on each of the above-mentioned thin-film elements for objectives such as process control and prevention of nonconforming products, wherein the wafer identifying information is used for identifying the wafer to which each of the thin-film elements belongs, and the element location identifying information is used for identifying the location of each of the thin-film elements on the wafer. These items of identification information are written on the wafer at a point before the wafer is divided into the respective thin-film elements. The identification information is also made of patterned films that are patterned through the use of photolithography, for example. Japanese Published Patent Application 62-20116 discloses a technique in which, on a wafer on which a plurality of thin-film magnetic heads are to be formed, marks for identifying the respective heads are formed in a batch by photolithography.
To write identifying information through the use of patterned films that are patterned through the use of photolithography, it is required to form the patterned films for identifying information at specific locations, using the alignment marks already formed as references indicating the locations. Consideration will now be given to a case in which identifying information is written on the wafer through the use of photolithography, using an alignment mark that is first formed (that may be hereinafter called the first alignment mark) as a reference indicating the location. This case may be one in which a patterned film for the first alignment mark and a patterned film for the identifying information are formed at the same heights by patterning a single thin film. In this case, according to the prior art, the patterned film for the first alignment mark is formed, and then a photolithography step for forming the patterned film for the identifying information is performed using the patterned film for the first alignment mark as the reference of the location.
The following is a description of an example of method of writing identifying information as a related-art method of writing identifying information, wherein the identifying information is written by photolithography using the first alignment mark as the reference of the location. FIG. 34 is a flowchart showing the related-art method of writing identifying information. FIG. 35A to FIG. 45A, FIG. 35B to FIG. 45B, FIG. 35C to FIG. 45C, and FIG. 35D to FIG. 45D are views for illustrating the steps of the method of writing identifying information of FIG. 34. FIG. 35A to FIG. 45A, FIG. 35B to FIG. 45B, FIG. 35C to FIG. 45C, and FIG. 35D to FIG. 45D each illustrate a state of a layered structure made up of a wafer and layers formed thereon. FIG. 35A to FIG. 45A each illustrate a top surface of a region in which the identifying information is to be located. FIG. 35B to FIG. 45B each illustrate a top surface of a region in which the first alignment mark is to be located. FIG. 35C to FIG. 45C each illustrate a cross section of the region in which the identifying information is to be located. FIG. 35D to FIG. 45D each illustrate a cross section of the region in which the first alignment mark is to be located. The region in which the identifying information is to be located may be a rectangular region, for example, surrounding the identifying information. Similarly, the region in which the first alignment mark is to be located may be a rectangular region, for example, surrounding the first alignment mark.
In the method of writing identifying information of FIG. 34, first, as shown in FIG. 35A to FIG. 35D, a metal film 212 is formed on the wafer 211 by sputtering, for example (step S201).
Next, as shown in FIG. 36A to FIG. 36D, a resist layer 214 is formed by applying a resist to the top of the metal film 212 (step S202). The resist used here may be positive one, for example.
Next, as shown in FIG. 37A to FIG. 37D, the resist layer 214 is exposed through masks 215 and 216 (step S203). The mask 215 is formed to intercept light in an entire region where the identifying information is to be located. The mask 216 is designed so that, in the region where the first alignment mark is to be located, light is intercepted in portions corresponding to the pattern of the first alignment mark, and light is allowed to pass through in the other portions.
Next, as shown in FIG. 38A to FIG. 38D, the resist layer 214 is developed (step S204). In the region where the identifying information is to be located, the resist layer 214 developed entirely remains. In the region where the first alignment mark is to be located, portions of the resist layer 214 developed that correspond to the pattern of the first alignment mark only remain. In FIG. 34 the steps surrounded by the broken line indicated with S21, that is, the steps from S202 to S204, are the photolithography steps for forming the first alignment mark.
Next, as shown in FIG. 39A to FIG. 39D, the metal film 212 is selectively etched, using the resist layer 214 as an etching mask (step S205). As a result, in the region where the identifying information is to be located, the metal film 212 entirely remains. In the region where the first alignment mark is to be located, portions of the metal film 212 that correspond to the pattern of the first alignment mark only remain. The portions of the metal film 212 remaining in the region where the first alignment mark is to be located become a patterned film 212A for the first alignment mark. Next, as shown in FIG. 40A to FIG. 40D, the resist layer 214 is removed (step S206).
Next, as shown in FIG. 41A to FIG. 41D, a resist layer 217 is formed by applying a resist to the entire top surface of the layered structure (step S207). The resist used here may be positive one, for example.
Next, as shown in FIG. 42A to FIG. 42D, the resist layer 217 is exposed through masks 218 and 219 (step S208). The mask 218 is designed so that, in the region where the identifying information is to be located, light is intercepted in portions corresponding to the pattern of the identifying information, and light is allowed to pass through in the other portions. The mask 219 is formed to intercept light in the entire region where the first alignment mark is to be located. In this step, the masks 218 and 219 are aligned using the patterned film 212A for the first alignment mark as the reference of the location.
Next, as shown in FIG. 43A to FIG. 43D, the resist layer 217 is developed (step S209). In the region where the identifying information is to be located, portions of the resist layer 217 developed that correspond to the pattern of the identifying information only remain. In the region where the first alignment mark is to be located, the resist layer 217 developed entirely remains. In FIG. 34 the steps surrounded by the broken line indicated with S22, that is, the steps from S207 to S209, are the photolithography steps for writing the identifying information.
Next, as shown in FIG. 44A to FIG. 44D, the metal film 212 is selectively etched, using the resist layer 217 as an etching mask (step S210). As a result, in the region where the identifying information is to be located, portions of the metal film 212 that correspond to the pattern of the identifying information only remain. These remaining portions of the metal film 212 become a patterned film 212B for the identifying information. In the region where the first alignment mark is to be located, the patterned film 212A remains as it is. Next, as shown in FIG. 45A to FIG. 45D, the resist layer 217 is removed (step S211), and the steps for writing the identifying information are thereby completed.
According to the related-art method of writing identifying information shown in FIG. 34, FIG. 35A to FIG. 45A, FIG. 35B to FIG. 45B, FIG. 35C to FIG. 45C, and FIG. 35D to FIG. 45D, there arises a problem that, since the method includes a great number of steps, a long period of time and costs are required for forming the patterned film for the first alignment mark and the patterned film for the identifying information.